Cerebral preconditioning and ischaemic tolerance

NADPH oxidase-2: linking glucose, acidosis, and excitotoxicity in stroke

SIGNIFICANCE

Neuronal superoxide production contributes to cell death in both glutamate excitotoxicity and brain ischemia (stroke). NADPH oxidase-2 (NOX2) is the major source of neuronal superoxide production in these settings, and regulation of NOX2 activity can thereby influence outcome in stroke.

RECENT ADVANCES

Reduced NOX2 activity can rescue cells from oxidative stress and cell death that otherwise occur in excitotoxicity and ischemia. NOX2 activity is regulated by several factors previously shown to affect outcome in stroke, including glucose availability, intracellular pH, protein kinase ζ/δ, casein kinase 2, phosphoinositide-3-kinase, Rac1/2, and phospholipase A2. The newly identified functions of these factors as regulators of NOX2 activity suggest alternative mechanisms for their effects on ischemic brain injury.

CRITICAL ISSUES

Key aspects of these regulatory influences remain unresolved, including the mechanisms by which rac1 and phospholipase activities are coupled to N-methyl-D-aspartate (NMDA) receptors, and whether superoxide production by NOX2 triggers subsequent superoxide production by mitochondria.

FUTURE DIRECTIONS

It will be important to establish whether interventions targeting the signaling pathways linking NMDA receptors to NOX2 in brain ischemia can provide a greater neuroprotective efficacy or a longer time window to treatment than provided by NMDA receptor blockade alone. It will likewise be important to determine whether dissociating superoxide production from the other signaling events initiated by NMDA receptors can mitigate the deleterious effects of NMDA receptor blockade.

Ethyl 3,4-dihydroxy benzoate, a unique preconditioning agent for alleviating hypoxia-mediated oxidative damage in L6 myoblasts cells

The importance of hypoxia inducible factor (HIF) as the master regulator of hypoxic responses is well established. Oxygen-dependent prolyl hydroxylase domain enzymes (PHDs) negatively regulate HIF directing it to the path of degradation under normoxia and are, consequently, attractive therapeutic targets. Inhibition of PHDs might upregulate beneficial HIF-mediated processes. In this study, we have examined the efficacy of PHD inhibitor ethyl 3,4-dihydroxy benzoate (EDHB) in affording protection against hypoxia-induced oxidative damage in L6 myoblast cells. L6 cells were exposed to hypoxia (0.5 % O2) after preconditioning with EDHB for different times. Levels of HIF-1α, oxidative stress and antioxidant status were measured after hypoxia exposure. Preconditioning with EDHB significantly improved cellular viability, and the diminished levels of protein oxidation and malondialdehyde indicated a decrease in oxidative stress when exposed to hypoxia. EDHB treatment also conferred enhanced anti-oxidant status, as there was an increase in the levels of glutathione and antioxidant enzymes like superoxide dismutase and glutathione peroxidase. Further, augmentation of the levels of HIF-1α boosted protein expression of antioxidative enzyme heme-oxygenase I. There was enhanced expression of metallothioneins which also have antioxidant, anti-inflammatory properties. These results thus accentuate the potential cytoprotective efficacy of EDHB against hypoxia-induced oxidative damage.

Preconditioning effect on cerebral vasospasm in patients with aneurysmal subarachnoid hemorrhage

BACKGROUND

Recent experimental evidence indicates that endogenous mechanisms against cerebral vasospasm can be induced via preconditioning.

OBJECTIVE

To determine whether these vascular protective mechanisms are also present in vivo in humans with aneurysmal subarachnoid hemorrhage.

METHODS

A multicenter retrospective cohort of patients with aneurysmal subarachnoid hemorrhage was examined for ischemic preconditioning stimulus: preexisting steno-occlusive cerebrovascular disease (CVD) and/or previous cerebral infarct. Generalized estimating equation models were performed to determine the effect of the preconditioning stimulus on the primary end points of radiographic vasospasm, symptomatic vasospasm, and vasospasm-related delayed cerebral infarction and the secondary end point of discharge modified Rankin Scale score.

RESULTS

Of 1043 patients, 321 (31%) had preexisting CVD and 437 (42%) had radiographic vasospasm. Patients with preexisting CVD were less likely to develop radiographic vasospasm (odds ratio = 0.67; 95% confidence interval = 0.489-0.930; P = .02) but had no differences in other end points. In terms of the secondary end point, patients with preexisting CVD did not differ significantly from patients without preexisting CVD in mortality or unfavorable outcome in multivariate analyses, although patients with preexisting CVD were marginally more likely to die (P = .06).

CONCLUSION

This retrospective case-control study suggests that endogenous protective mechanisms against cerebral vasospasm-a preconditioning effect-may exist in humans, although these results could be the effect of atherosclerosis or some combination of preconditioning and atherosclerosis. Additional studies investigating the potential of preconditioning in aneurysmal subarachnoid hemorrhage are warranted.

A comparative immunological analysis of CoCl2 treated cells with in vitro hypoxic exposure

The hypoxic preconditioning of mammalian cells has been shown to have beneficial effects against hypoxic injuries. However, very little information is available on the comparative analysis of immunological responses to hypoxic and hypoxia mimetic exposure. Therefore, in the present study, mouse peritoneal macrophages and splenocytes were subjected to hypoxia exposure (0.5 % O2) and hypoxia mimetic Cobalt chloride (CoCl2) treatment to evaluate their effect on immune response and delineate the underlying signaling mechanisms. The results obtained indicated that super oxide generation increased while TLR4 expression and cell surface markers like CD25, CD40 and CD69 were suppressed in both the treatments as compared to normoxia. Cobalt chloride treatment increased NF-κB expression, nitric oxide (NO) and iNOS expression, cytokines TNF-α and IL-6 as compared to hypoxia exposure. Our study showed that CoCl2 stabilizes HIF-1α to create hypoxia like conditions but it mainly influences the inflammatory response via NF-κB signaling pathway by skewing the production of proinflammatory molecules like TNF-α, IL-6 and NO.

Oleanolic Acid enhances the beneficial effects of preconditioning on PC12 cells

Preconditioning triggers endogenous protection against subsequent exposure to higher concentrations of a neurotoxin. In this study, we investigated whether exposure to oleanolic acid (OA) enhances the protective effects of preconditioning on PC12 cells exposed to 6-hydroxydopamine (6-OHDA). A concentration response curve was constructed using 6-OHDA (50, 150, 300, and 600 μM). The experiment consisted of 6 groups: untreated, OA only, Group 1: cells treated with 6-OHDA (50 μM) for 1 hour, Group 2: cells treated with 6-OHDA (150 μM) for 1 hour, Group 3: cells treated with 6-OHDA (50 μM) for 30 minutes followed 6 hours later by treatment with 6-OHDA (150 μM) for 30 minutes, and Group 4: cells treated as in group 3 but also received OA immediately after the second 6-OHDA treatment. Cell viability and apoptotic ratio were assessed using the MTT and Annexin V staining tests, respectively. In preconditioned cells, we found that cell viability remained high following exposure to 6-OHDA (150 μM). OA treatment enhanced the protective effects of preconditioning. Similarly, with the annexin V apoptosis test, preconditioning protected the cell and this was enhanced by OA. Therefore, preexposure of PC12 cells to low 6-OHDA concentration can protect against subsequent toxic insults of 6-OHDA and OA enhances this protection.

KATP-channels play a minor role in the protective hypoxic shut-down of cerebellar activity in eider ducks (Somateria mollissima)

Eider duck (Somateria mollissima) cerebellar neurons are highly tolerant toward hypoxia in vitro, which in part is due to a hypoxia-induced depression of their spontaneous activity. We have studied whether this response involves ATP-sensitive potassium (KATP) channels, which are known to be involved in the hypoxic/ischemic defense of mammalian neural and muscular tissues, by causing hyperpolarization and reduced ATP demand. Extracellular recordings in the Purkinje layer of isolated normoxic eider duck cerebellar slices showed that their spontaneous neuronal activity decreased significantly compared to in control slices when the KATP channel opener diazoxide (600 μM) was added (F1,70=92.781, p<0.001). Adding the KATP channel blocker tolbutamide (400 μM) 5 min prior to diazoxide completely abolished its effect (F1,55=39.639, p<0.001), strongly suggesting that these drugs have a similar mode of action in this avian species as in mammals. The spontaneous activity of slices treated with tolbutamide in combined hypoxia/chemical anoxia (95% N2-5% CO2 and 2 mM NaCN) was not significantly different from that of control slices (F1,203=0.071, p=0.791). Recovery from hypoxia/anoxia was, however, slightly but significantly weaker in tolbutamide-treated slices than in control slices (F1,137=15.539, p<0.001). We conclude that KATP channels are present in eider duck cerebellar neurons and are activated in hypoxia/anoxia, but that they do not play a key role in the protective shut-down response to hypoxia/anoxia.

Metformin attenuates blood-brain barrier disruption in mice following middle cerebral artery occlusion

BACKGROUND

Metformin, a widely used hypoglycemic drug, reduces stroke incidence and alleviates chronic inflammation in clinical trials. However, the effect of metformin in ischemic stroke is unclear. Here, we investigated the effect of metformin on ischemic stroke in mice and further explored the possible underlying mechanisms.

METHODS

Ninety-eight adult male CD-1 mice underwent 90-minute transient middle cerebral artery occlusion (tMCAO). Metformin (200 mg/kg) was administrated for up to 14 days. Neurobehavioral outcomes, brain infarct volume, inflammatory factors, blood-brain barrier (BBB) permeability and AMPK signaling pathways were evaluated following tMCAO. Oxygen glucose deprivation was performed on bEND.3 cells to explore the mechanisms of metformin in inhibiting inflammatory signaling pathways.

RESULTS

Infarct volume was reduced in metformin-treated mice compared to the control group following tMCAO (P < 0.05). Neurobehavioral outcomes were greatly improved in metformin-treated mice (P < 0.05). MPO+ cells, Gr1+ cells, MPO activity and BBB permeability were decreased after metformin administration (P < 0.05). In addition, metformin activated AMPK phosphorylation, inhibited NF-κB activation, down-regulated cytokine (IL-1β, IL-6, TNF-α) and ICAM-1 expression following tMCAO (P < 0.05). Furthermore, metformin activated AMPK signaling pathway and alleviated oxygen-glucose deprivation-induced ICAM-1 expression in bEND.3 cells (P < 0.05). Compound C, a selective AMPK inhibitor, eliminated this promotional effect.

CONCLUSIONS

Metformin down-regulated ICAM-1 in an AMPK-dependent manner, which could effectively prevent ischemia-induced brain injury by alleviating neutrophil infiltration, suggesting that metformin is a promising therapeutic agent in stroke therapy.

Effects of ischemic preconditioning on VEGF and pFlk-1 immunoreactivities in the gerbil ischemic hippocampus after transient cerebral ischemia

Ischemia preconditioning (IPC) displays an important adaptation of the CNS to sub-lethal ischemia. In the present study, we examined the effect of IPC on immunoreactivities of VEGF-, and phospho-Flk-1 (pFlk-1) following transient cerebral ischemia in gerbils. The animals were randomly assigned to four groups (sham-operated-group, ischemia-operated-group, IPC plus (+) sham-operated-group, and IPC+ischemia-operated-group). IPC was induced by subjecting gerbils to 2 min of ischemia followed by 1 day of recovery. In the ischemia-operated-group, a significant loss of neurons was observed in the stratum pyramidale (SP) of the hippocampal CA1 region (CA1) alone 5 days after ischemia-reperfusion, however, in all the IPC+ischemia-operated-groups, pyramidal neurons in the SP were well protected. In immunohistochemical study, VEGF immunoreactivity in the ischemia-operated-group was increased in the SP at 1 day post-ischemia and decreased with time. Five days after ischemia-reperfusion, strong VEGF immunoreactivity was found in non-pyramidal cells, which were identified as pericytes, in the stratum oriens (SO) and radiatum (SR). In the IPC+sham-operated- and IPC+ischemia-operated-groups, VEGF immunoreactivity was significantly increased in the SP. pFlk-1 immunoreactivity in the sham-operated- and ischemia-operated-groups was hardly found in the SP, and, from 2 days post-ischemia, pFlk-1 immunoreactivity was strongly increased in non-pyramidal cells, which were identified as pericytes. In the IPC+sham-operated-group, pFlk-1 immunoreactivity was significantly increased in both pyramidal and non-pyramidal cells; in the IPC+ischemia-operated-groups, the similar pattern of VEGF immunoreactivity was found in the ischemic CA1, although the VEGF immunoreactivity was strong in non-pyramidal cells at 5 days post-ischemia. In brief, our findings show that IPC dramatically augmented the induction of VEGF and pFlk-1 immunoreactivity in the pyramidal cells of the CA1 after ischemia-reperfusion, and these findings suggest that the increases of VEGF and Flk-1 expressions may be necessary for neurons to survive from transient ischemic damage.

Effects of hypoxic preconditioning on synaptic ultrastructure in mice

Hypoxic preconditioning (HPC) elicits resistance to more drastic subsequent insults, which potentially provide neuroprotective therapeutic strategy, but the underlying mechanisms remain to be fully elucidated. Here, we examined the effects of HPC on synaptic ultrastructure in olfactory bulb of mice. Mice underwent up to five cycles of repeated HPC treatments, and hypoxic tolerance was assessed with a standard gasp reflex assay. As expected, HPC induced an increase in tolerance time. To assess synaptic responses, Western blots were used to quantify protein levels of representative markers for glia, neuron, and synapse, and transmission electron microscopy was used to examine synaptic ultrastructure and mitochondrial density. HPC did not significantly alter the protein levels of astroglial marker (GFAP), neuron-specific markers (GAP43, Tuj-1, and OMP), synaptic number markers (synaptophysin and SNAP25) or the percentage of excitatory synapses versus inhibitory synapses. However, HPC significantly affected synaptic curvature and the percentage of synapses with presynaptic mitochondria, which showed concomitant change pattern. These findings demonstrate that HPC is associated with changes in synaptic ultrastructure.

Ischemic preconditioning reduces ischemic brain injury by suppressing nuclear factor kappa B expression and neuronal apoptosis

Ischemic stroke induces a series of complex pathophysiological events including blood-brain barrier disruption, inflammatory response and neuronal apoptosis. Previous studies demonstrate that ischemic preconditioning attenuates ischemic brain damage via inhibiting blood-brain barrier disruption and the inflammatory response. Rats underwent transient (15 minutes) occlusion of the bilateral common carotid artery with 48 hours of reperfusion, and were subjected to permanent middle cerebral artery occlusion. This study explored whether ischemic preconditioning could reduce ischemic brain injury and relevant molecular mechanisms by inhibiting neuronal apoptosis. Results found that at 72 hours following cerebral ischemia, myeloperoxidase activity was enhanced, malondialdehyde levels increased, and neurological function was obviously damaged. Simultaneously, neuronal apoptosis increased, and nuclear factor-κB and cleaved caspase-3 expression was significantly increased in ischemic brain tissues. Ischemic preconditioning reduced the cerebral ischemia-induced inflammatory response, lipid peroxidation, and neurological function injury. In addition, ischemic preconditioning decreased nuclear factor-κB p65 and cleaved caspase-3 expression. These results suggested that ischemic preconditioning plays a protective effect against ischemic brain injury by suppressing the inflammatory response, reducing lipid peroxidation, and neuronal apoptosis via inhibition of nuclear factor-κB and cleaved caspase-3 expression.

Role of iron in ischemia-induced neurodegeneration: mechanisms and insights

Iron is an important micronutrient for neuronal function and survival. It plays an essential role in DNA and protein synthesis, neurotransmission and electron transport chain due to its dual redox states. On the contrary, iron also catalyses the production of free radicals and hence, causes oxidative stress. Therefore, maintenance of iron homeostasis is very crucial and it involves a number of proteins in iron metabolism and transport that maintain the balance. In ischemic conditions large amount of iron is released and this free iron catalyzes production of more free radicals and hence, causing more damage. In this review we have focused on the iron transport and maintenance of iron homeostasis at large and also the effect of imbalance in iron homeostasis on retinal and brain tissue under ischemic conditions. The understanding of the proteins involved in the homeostasis imbalance will help in developing therapeutic strategies for cerebral as well retinal ischemia.

3-Nitropropionic acid-induced ischemia tolerance in the rat brain is mediated by reduced metabolic activity and cerebral blood flow

Tissue tolerance to ischemia can be achieved by noxious stimuli that are below a threshold to cause irreversible damage ('preconditioning'). Understanding the mechanisms underlying preconditioning may lead to the identification of novel therapeutic targets for diseases such as stroke. We here used the oxidative chain inhibitor 3-nitropropionic acid (NPA) to induce ischemia tolerance in a rat middle cerebral artery occlusion (MCAO) stroke model. Cerebral blood flow (CBF) and structural integrity were characterized by longitudinal magnetic resonance imaging (MRI) in combination with behavioral, histologic, and biochemical assessment of NPA-preconditioned animals and controls. Using this approach we show that the ischemia-tolerant state is characterized by a lower energy charge potential and lower CBF, indicating a reduced baseline metabolic demand, and therefore a cellular mechanism of neural protection. Blood vessel density and structural integrity were not altered by NPA treatment. When subjected to MCAO, preconditioned animals had a characteristic MRI signature consisting of enhanced CBF maintenance within the ischemic territory and intraischemic reversal of the initial cytotoxic edema, resulting in reduced infarct volumes. Thus, our data show that tissue protection through preconditioning occurs early during ischemia and indicate that a reduced cellular metabolism is associated with tissue tolerance to ischemia.

Induction of ischemic tolerance as a promising treatment against diabetic retinopathy

Diabetic retinopathy is a leading cause of acquired blindness, and it is the most common ischemic disorder of the retina. Available treatments are not very effective. Efforts to inhibit diabetic retinopathy have focused either on highly specific therapeutic approaches for pharmacologic targets or using genetic approaches to change expression of certain enzymes. However, it might be wise to choose innovative treatment modalities that act by multiple potential mechanisms. The resistance to ischemic injury, or ischemic tolerance, can be transiently induced by prior exposure to a non-injurious preconditioning stimulus. A complete functional and histologic protection against retinal ischemic damage can be achieved by previous preconditioning with non-damaging ischemia. In this review, we will discuss evidence that supports that ischemic conditioning could help avert the dreaded consequences that results from retinal diabetic damage.

Biological networks in ischemic tolerance - rethinking the approach to clinical conditioning

The adaptive response (conditioning) to environmental stressors evokes evolutionarily conserved programs in uni- and multicellular organisms that result in increased fitness and resistance to stressor induced injury. Although the concept of conditioning has been around for a while, its translation into clinical therapies targeting neurovascular diseases has only recently begun. The slow pace of clinical adoption might be partially explained by our poor understanding of underpinning mechanisms and of the complex responses of the organism to the stressor. At the 2(nd) Translational Preconditioning Meeting participants engaged in an intense discussion addressing whether the time has come to more aggressively implement clinical conditioning protocols in the treatment of cerebrovascular diseases or whether it would be better to wait until preclinical data would help to minimize clinical empiricism. This review addresses the complex involvement of biological networks in establishing ischemic tolerance at the organism level using two clinically promising conditioning modalities, namely remote ischemic preconditioning, and per- or post-conditioning, as examples.

Should the STAIR criteria be modified for preconditioning studies?

Diverse preconditioning (PC) stimuli protect against a wide variety of neuronal insults in animal models, engendering enthusiasm that PC could be used to protect the brain clinically. Candidate clinical applications include cardiac and vascular surgery, after subarachnoid hemorrhage, and prior to conditions in which acute neuronal injury is anticipated. However, disappointments in clinical validation of multiple neuroprotectants suggest potential problems translating animal data into successful human therapies. Thus, despite strong promise of preclinical PC studies, caution should be maintained in translating these findings into clinical applications. The Stroke Therapy Academic Industry Roundtable (STAIR) working group and the National institute of Neurological Diseases and Stroke (NINDS) proposed working guidelines to improve the utility of preclinical studies that form the foundation of therapies for neurological disease. Here, we review the applicability of these consensus criteria to preconditioning studies and discuss additional considerations for PC studies. We propose that special attention should be paid to several areas, including 1) safety and dosage of PC treatments; 2) meticulously matching preclinical modeling to the human condition to be tested; and 3) timing of both the initiation and discontinuation of the PC stimulus relative to injury ictus.

miR-21 in ischemia/reperfusion injury: a double-edged sword?

MicroRNAs (miRNAs or miRs) are endogenous, small RNA molecules that suppress expression of targeted mRNA. miR-21, one of the most extensively studied miRNAs, is importantly involved in divergent pathophysiological processes relating to ischemia/reperfusion (I/R) injury, such as inflammation and angiogenesis. The role of miR-21 in renal I/R is complex, with both protective and pathological pathways being regulated by miR-21. Preconditioning-induced upregulation of miR-21 contributes to the protection against subsequent renal I/R injury through the targeting of genes such as the proapoptotic gene programmed cell death 4 and interactions between miR-21 and hypoxia-inducible factor. Conversely, long-term elevation of miR-21 may be detrimental to the organ by promoting the development of renal interstitial fibrosis following I/R injury. miR-21 is importantly involved in several pathophysiological processes related to I/R injury including inflammation and angiogenesis as well as the biology of stem cells that could be used to treat I/R injury; however, the effect of miR-21 on these processes in renal I/R injury remains to be studied.

Transient ischemia elicits a sustained enhancement of thrombus development in the cerebral microvasculature: effects of anti-thrombotic therapy

OBJECTIVE

While transient ischemic attack (TIA) is a well-known harbinger of ischemic stroke, the mechanisms that link TIA to subsequent strokes remain poorly understood. The overall aim of this study was to determine whether: 1) brief periods of transient cerebral ischemia render this tissue more vulnerable to thrombus development and 2) antiplatelet agents used in TIA patients alter ischemia-induced thrombogenesis.

APPROACH & RESULTS

The middle cerebral artery of C57BL/6 mice was occluded for 2.5-10min, followed by reperfusion periods of 1-28days. Intravital microscopy was used to monitor thrombus development in cerebral microvessels induced by light/dye photoactivation. Thrombosis was quantified as the time to platelet aggregation on the vessel wall and the time for complete blood flow cessation. While brief periods of cerebral ischemia were not associated with neurological deficits or brain infarction (evaluated after 1day), it yielded a pronounced and prolonged (up to 28days) acceleration of thrombus formation, compared to control (sham) mice. This prothrombotic phenotype was not altered by pre- and/or post-treatment of mice with either aspirin (A), clopidogrel (C), dipyridamole (D), or atorvastatin (S), or with A+D+S.

CONCLUSIONS

The increased vulnerability of the cerebral vasculature to thrombus development after a brief period of transient ischemia can be recapitulated in a murine model. Antiplatelet or antithrombotic agents used in patients with TIA show no benefit in this mouse model of brief transient ischemia.

HIF prolyl hydroxylase inhibition prior to transient focal cerebral ischaemia is neuroprotective in mice

This study investigated the effects of 2-(1-chloro-4-hydroxyisoquinoline-3-carboxamido) acetic acid (IOX3), a selective small molecule inhibitor of hypoxia-inducible factor (HIF) prolyl hydroxylases, on mouse brains subject to transient focal cerebral ischaemia. Male, 8- to 12-week-old C57/B6 mice were subjected to 45 min of middle cerebral artery occlusion (MCAO) either immediately or 24 h after receiving IOX3. Mice receiving IOX3 at 20 mg/kg 24 h prior to the MCAO had better neuroscores and smaller blood-brain barrier (BBB) disruption and infarct volumes than mice receiving the vehicle, whereas those having IOX3 at 60 mg/kg showed no significant changes. IOX3 treatment immediately before MCAO was not neuroprotective. IOX3 up-regulated HIF-1α, and increased EPO expression in mouse brains. In an in vitro BBB model (RBE4 cell line), IOX3 up-regulated HIF-1α and delocalized ZO-1. Pre-treating IOX3 on RBE4 cells 24 h before oxygen-glucose deprivation had a protective effect on endothelial barrier preservation with ZO-1 being better localized, while immediate IOX3 treatment did not. Our study suggests that HIF stabilization with IOX3 before cerebral ischaemia is neuroprotective partially because of BBB protection, while immediate application could be detrimental. These results provide information for studies aimed at the therapeutic activation of HIF pathway for neurovascular protection from cerebral ischaemia. We show that IOX3, a selective small molecule (280.66 Da) HIF prolyl hydroxylase inhibitor, could up-regulate HIF-1α and increase erythropoietin expression in mice. We further demonstrate that HIF stabilization with IOX3 before cerebral ischaemia is neuroprotective partially because of blood-brain barrier (BBB) protection, while immediate application is detrimental both in vivo and in vitro. These findings provide new insights into the role of HIF stabilization in ischaemic stroke.

Ischemic tolerance modulates TRAIL expression and its receptors and generates a neuroprotected phenotype

TNF-related apoptosis inducing ligand (TRAIL), a member of the TNF superfamily released by microglia, appears to be involved in the induction of apoptosis following focal brain ischemia. Indeed, brain ischemia is associated with progressive enlargement of damaged areas and prominent inflammation. As ischemic preconditioning reduces inflammatory response to brain ischemia and ameliorates brain damage, the purpose of the present study was to evaluate the role of TRAIL and its receptors in stroke and ischemic preconditioning and to propose, by modulating TRAIL pathway, a new therapeutic strategy in stroke. In order to achieve this aim a rat model of harmful focal ischemia, obtained by subjecting animals to 100 min of transient occlusion of middle cerebral artery followed by 24 h of reperfusion and a rat model of ischemic preconditioning in which the harmful ischemia was preceded by 30 mins of tMCAO, which represents the preconditioning protective stimulus, were used. Results show that the neuroprotection elicited by ischemic preconditioning occurs through both upregulation of TRAIL decoy receptors and downregulation of TRAIL itself and of its death receptors. As a counterproof, immunoneutralization of TRAIL in tMCAO animals resulted in significant restraint of tissue damage and in a marked functional recovery. Our data shed new light on the mechanisms that propagate ongoing neuronal damage after ischemia in the adult mammalian brain and provide new molecular targets for therapeutic intervention. Strategies aimed to repress the death-inducing ligands TRAIL, to antagonize the death receptors, or to activate the decoy receptors open new perspectives for the treatment of stroke.

Post-conditioning and reperfusion injury in the treatment of stroke

Endogenous mechanisms of protection against ischemia can be demonstrated in brain and other organs. The induction of such protection is via a response to sub lethal stress which induces "preconditioning". The preconditioned organ is then "tolerant" to injury from subsequent severe stress of the same or different etiology. Protection is substantial (70% reduction) but delayed in onset and is transient. Gene expression is unique between brains preconditioned, injured (stroke) or made tolerant. Thus, preconditioning reprograms the response to lethal ischemic stress (stroke), reprogrammed from an injury induction response to a neuroprotective processes. Postconditioning refers to attenuation of injurious processes occurring during reperfusion of ischemic brain. Transient mechanical interruption of reperfusion induces post-conditioning which can attenuate reperfusion injury. Post-conditioning protects ischemic brain by decreasing reperfusion induced oxygen free radical formation. The free radicals produce injury via mitochondrial damage which can be repaired experimentally. Post-conditioning produces neuroprotection as potent as experimental preconditioning. The recognition of broad based gene silencing (suppression of thousands of genes) as the phenotype of the preconditioned, ischemic tolerant brain, may explain failure of all single target drugs for stroke. As risks of reperfusion injury accompany treatment for acute stroke, endogenous neuroprotective and repair mechanisms offer translational stroke therapy.

The effects of hypoxic preconditioning on white matter damage following hypoxic-ischaemic injury in the neonatal rat brain

Myelination is an essential process in human development that is carried out by oligodendrocytes in the central nervous system. Hypoxic-ischaemic (HI) brain injury can disrupt myelination by causing oxidative stress, inflammation and excitotoxicity, resulting in the loss of myelin as well as cells of the oligodendrocyte lineage. We have previously shown that hypoxic preconditioning (HP) can protect against HI injury, however, to date there have been no reports of its effects on white matter injury. Sprague-Dawley rat pups (postnatal day (P) 6) were placed into control and HP groups. On P7, pups were further separated into HI and sham surgery groups. HI pups underwent a unilateral common carotid artery occlusion and then exposed to 8% oxygen for 3h. Sham pups underwent the same procedure without occlusion and were maintained in room air. Brains were removed 5 days post-surgery for analysis. In HI-only pups there was a significant reduction in brain volume observed. Consequently, when HP was performed prior to HI, the loss of brain tissue was prevented. The number of early and late oligodendrocyte progenitors (preOLs) in the corpus callosum was unaffected by HI, however, HI reduced the amount of myelin basic protein, indicating that HI may inhibit the maturation of preOLs. Whilst HP did not affect preOL density, it was found to prevent the loss of myelin caused by HI. This indicates that HP may either protect myelin directly or possibly promote the maturation of preOLs to regenerate the lost or damaged myelin.

Mitochondria: a multimodal hub of hypoxia tolerance

Decreased oxygen availability impairs cellular energy production and, without a coordinated and matched decrease in energy consumption, cellular and whole organism death rapidly ensues. Of particular interest are mechanisms that protect brain from low oxygen injury, as this organ is not only the most sensitive to hypoxia, but must also remain active and functional during low oxygen stress. As a result of natural selective pressures, some species have evolved molecular and physiological mechanisms to tolerate prolonged hypoxia with no apparent detriment. Among these mechanisms are a handful of responses that are essential for hypoxia tolerance, including (i) sensors that detect changes in oxygen availability and initiate protective responses; (ii) mechanisms of energy conservation; (iii) maintenance of basic brain function; and (iv) avoidance of catastrophic cell death cascades. As the study of hypoxia-tolerant brain progresses, it is becoming increasingly apparent that mitochondria play a central role in regulating all of these critical mechanisms. Furthermore, modulation of mitochondrial function to mimic endogenous neuroprotective mechanisms found in hypoxia-tolerant species confers protection against otherwise lethal hypoxic stresses in hypoxia-intolerant organs and organisms. Therefore, lessons gleaned from the investigation of endogenous mechanisms of hypoxia tolerance in hypoxia-tolerant organisms may provide insight into clinical pathologies related to low oxygen stress.

Spreading depression requires microglia and is decreased by their M2a polarization from environmental enrichment

Microglia play an important role in fine-tuning neuronal activity. In part, this involves their production of tumor necrosis factor-alpha (TNFα), which increases neuronal excitability. Excessive synaptic activity is necessary to initiate spreading depression (SD). Increased microglial production of proinflammatory cytokines promotes initiation of SD, which, when recurrent, may play a role in conversion of episodic to high frequency and chronic migraine. Previous work shows that this potentiation of SD occurs through increased microglial production of TNFα and reactive oxygen species, both of which are associated with an M1-skewed microglial population. Hence, we explored the role of microglia and their M1 polarization in SD initiation. Selective ablation of microglia from rat hippocampal slice cultures confirmed that microglia are essential for initiation of SD. Application of minocycline to dampen M1 signaling led to increased SD threshold. In addition, we found that SD threshold was increased in rats exposed to environmental enrichment. These rats had increased neocortical levels of interleukin-11 (IL-11), which decreases TNFα signaling and polarized microglia to an M2a-dominant phenotype. M2a microglia reduce proinflammatory signaling and increase production of anti-inflammatory cytokines, and therefore may protect against SD. Nasal administration of IL-11 to mimic effects of environmental enrichment likewise increased M2a polarization and increased SD threshold, an effect also seen in vitro. Similarly, application of conditioned medium from M2a polarized primary microglia to slice cultures also increased SD threshold. Thus, microglia and their polarization state play an essential role in SD initiation, and perhaps by extension migraine with aura and migraine.

The histone lysine demethylase Kdm6b is required for activity-dependent preconditioning of hippocampal neuronal survival

Enzymes that regulate histone lysine methylation play important roles in neuronal differentiation, but little is known about their contributions to activity-regulated gene transcription in differentiated neurons. We characterized activity-regulated expression of lysine demethylases and lysine methyltransferases in the hippocampus of adult male mice following pilocarpine-induced seizure. Pilocarpine drove a 20-fold increase in mRNA encoding the histone H3 lysine 27-specific demethylase Kdm6b selectively in granule neurons of the dentate gyrus, and this induction was recapitulated in cultured hippocampal neurons by bicuculline and 4-aminopyridine (Bic + 4AP) stimulation of synaptic activity. Because activity-regulated gene expression is highly correlated with neuronal survival, we tested the requirement for Kdm6b expression in Bic + 4AP induced preconditioning of neuronal survival. Prior exposure to Bic + 4AP promoted neuronal survival in control neurons upon growth factor withdrawal; however, this effect was ablated when we knocked down Kdm6b expression. Loss of Kdm6b did not disrupt activity-induced expression of most genes, including that of a gene set previously established to promote neuronal survival in this assay. However, using bioinformatic analysis of RNA sequencing data, we discovered that Kdm6b knockdown neurons showed impaired inducibility of a discrete set of genes annotated for their function in inflammation. These data reveal a novel function for Kdm6b in activity-regulated neuronal survival, and they suggest that activity- and Kdm6b-dependent regulation of inflammatory gene pathways may serve as an adaptive pro-survival response to increased neuronal activity.

Mitochondrial reactive oxygen species: a double edged sword in ischemia/reperfusion vs preconditioning

Reductions in the blood supply produce considerable injury if the duration of ischemia is prolonged. Paradoxically, restoration of perfusion to ischemic organs can exacerbate tissue damage and extend the size of an evolving infarct. Being highly metabolic organs, the heart and brain are particularly vulnerable to the deleterious effects of ischemia/reperfusion (I/R). While the pathogenetic mechanisms contributing to I/R-induced tissue injury and infarction are multifactorial, the relative importance of each contributing factor remains unclear. However, an emerging body of evidence indicates that the generation of reactive oxygen species (ROS) by mitochondria plays a critical role in damaging cellular components and initiating cell death. In this review, we summarize our current understanding of the mechanisms whereby mitochondrial ROS generation occurs in I/R and contributes to myocardial infarction and stroke. In addition, mitochondrial ROS have been shown to participate in preconditioning by several pharmacologic agents that target potassium channels (e.g., ATP-sensitive potassium (mKATP) channels or large conductance, calcium-activated potassium (mBKCa) channels) to activate cell survival programs that render tissues and organs more resistant to the deleterious effects of I/R. Finally, we review novel therapeutic approaches that selectively target mROS production to reduce postischemic tissue injury, which may prove efficacious in limiting myocardial dysfunction and infarction and abrogating neurocognitive deficits and neuronal cell death in stroke.

Mitochondrial mechanisms in cerebral vascular control: shared signaling pathways with preconditioning

Mitochondrial-initiated events protect the neurovascular unit against lethal stress via a process called preconditioning, which independently promotes changes in cerebrovascular tone through shared signaling pathways. Activation of adenosine triphosphate (ATP)-dependent potassium channels on the inner mitochondrial membrane (mitoKATP channels) is a specific and dependable way to induce protection of neurons, astroglia, and cerebral vascular endothelium. Through the opening of mitoKATP channels, mitochondrial depolarization leads to activation of protein kinases and transient increases in cytosolic calcium (Ca(2+)) levels that activate terminal mechanisms that protect the neurovascular unit against lethal stress. The release of reactive oxygen species from mitochondria has similar protective effects. Signaling elements of the preconditioning pathways also are involved in the regulation of vascular tone. Activation of mitoKATP channels in cerebral arteries causes vasodilation, with cell-specific contributions from the endothelium, vascular smooth muscles, and nerves. Preexisting chronic conditions, such as insulin resistance and/or diabetes, prevent preconditioning and impair relaxation to mitochondrial-centered responses in cerebral arteries. Surprisingly, mitochondrial activation after anoxic or ischemic stress appears to protect cerebral vascular endothelium and promotes the restoration of blood flow; therefore, mitochondria may represent an important, but underutilized target in attenuating vascular dysfunction and brain injury in stroke patients.

Ischemic preconditioning provides neuroprotection by induction of AMP-activated protein kinase-dependent autophagy in a rat model of ischemic stroke

Accumulating evidence suggests that ischemic preconditioning (IPC) increases cerebral tolerance to the subsequent ischemic exposure. However, the underlying mechanisms are still not fully understood. In the present study, we tested the hypothesis that AMP-activated protein kinase (AMPK)-dependent autophagy contributed to the neuroprotection of IPC in rats with permanent cerebral ischemia. Male Sprague-Dawley rats were pretreated with vehicle, compound C (an AMPK inhibitor), or 3-methyladenine (3-MA, an autophagy inhibitor) and then were subjected to IPC induced by a 10-min middle cerebral artery occlusion. Afterward, the brain AMPK activity and autophagy biomarkers were measured. At 24 h after IPC, permanent cerebral ischemia was induced in these rats, and infarct volume, neurological deficits as well as cell apoptosis were evaluated 24 h later. We demonstrated that IPC activated AMPK and induced autophagy in the brain, which was accompanied by a reduction of infract volume, neurological deficits, and cell apoptosis after cerebral ischemia. Meanwhile, the IPC-induced autophagy was inhibited by compound C while the neuroprotection of IPC was abolished by compound C or 3-MA. These findings suggest that AMPK-mediated autophagy contributes to the neuroprotection of IPC, highlighting AMPK as a therapeutic target for stroke prevention and treatment.

Sarcosine preconditioning induces ischemic tolerance against global cerebral ischemia

Brain ischemic tolerance is an endogenous protective mechanism activated by a preconditioning stimulus that is closely related to N-methyl-d-aspartate receptor (NMDAR). Glycine transporter type 1 (GlyT-1) inhibitors potentiate NMDAR and suggest an alternative strategy for brain preconditioning. The aim of this work was to evaluate the effects of brain preconditioning induced by sarcosine, a GlyT-1 inhibitor, against global cerebral ischemia and its relation to NMDAR. Sarcosine was administered over 7 days (300 or 500 mg/kg/day, ip) before the induction of a global cerebral ischemia model in Wistar rats (male, 8-week-old). It was observed that sarcosine preconditioning reduced cell death in rat hippocampi submitted to cerebral ischemia. Hippocampal levels of glycine were decreased in sarcosine-treated animals, which was associated with a reduction of [(3)H] glycine uptake and a decrease in glycine transporter expression (GlyT-1 and GlyT-2). The expression of glycine receptors and the NR1 and NR2A subunits of NMDAR were not affected by sarcosine preconditioning. However, sarcosine preconditioning reduced the expression of the NR2B subunits of NMDAR. In conclusion, these data demonstrate that sarcosine preconditioning induces ischemic tolerance against global cerebral ischemia and this neuroprotective state is associated with changes in glycine transport and reduction of NR2B-containing NMDAR expression.

A double-edged sword: volatile anesthetic effects on the neonatal brain

The use of volatile anesthetics, a group of general anesthetics, is an exceedingly common practice. These anesthetics may have neuroprotective effects. Over the last decade, anesthetic induced neurotoxicity in pediatric populations has gained a certain notoriety based on pre-clinical cell and animal studies demonstrating that general anesthetics may induce neurotoxicity, including neuroapoptosis, neurodegeneration, and long-term neurocognitive and behavioral deficits. With hundreds of millions of people having surgery under general anesthesia worldwide, and roughly six million children annually in the U.S. alone, the importance of clearly defining toxic or protective effects of general anesthetics cannot be overstated. Yet, with our expanding body of knowledge, we have come to learn that perhaps not all volatile anesthetics have the same pharmacological profiles; certain ones may have a more favorable neurotoxic profile and may actually exhibit neuroprotection in specific populations and situations. Thus far, very few clinical studies exist, and have not yet been convincing enough to alter our practice. This review will provide an update on current data regarding volatile anesthetic induced neurotoxicity and neuroprotection in neonatal and infant populations. In addition, this paper will discuss ongoing studies and the trajectory of further research over the coming years.

Transferred inter-cell ischemic preconditioning-induced neuroprotection may be mediated by adenosine A1 receptors

Ischemic preconditioning-induced neuroprotection is a well-known phenomenon. We hypothesize that this form of neuroprotection is transferable among the same type of cells. To test this hypothesis, human neuroblastoma SH-SY5Y cells were induced to become neuron-like cells. Primary rat cortical neuronal cultures were also used. These cells were subjected to various lengths of short oxygen-glucose deprivation (OGD, an in vitro simulation of ischemia) and then 1-h OGD. Some cells that were not exposed to a short episode of ischemia were incubated with culture medium from the cells that had 3- or 5-min OGD. Those cells were subjected to OGD for 1h at 1 or 24h after they were exposed to the medium. Cell injury was evaluated at 24h after the 1-h OGD by lactate dehydrogenase release assay. In another experiment, cells subjected to a 3-min OGD or exposed to the medium from cells that had a 3-min OGD were harvested at 30min after the OGD or the medium exposure for Western blotting of Akt, a prosurvival protein. Our study showed that a prior episode of ischemia lasting from 3 to 10min significantly reduced the 1-h OGD-induced cell injury. Medium from cells subjected to a 3-min OGD also induced acute and delayed phases of neuroprotection in OGD-naïve human neuron-like cells and primary rat cortical neuronal cultures. Cells subjected to a 3-min OGD or incubated with the medium from cells exposed to a 3-min OGD had increased phosphorylated/activated Akt. The increased phosphorylated Akt and neuroprotection induced by medium transferring were inhibited by 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), an adenosine A1 receptor inhibitor. The 3-min OGD-induced neuroprotection was inhibited by LY294002, an Akt activation inhibitor. These results suggest that ischemic preconditioning-induced neuroprotection is transferable among the cells. Small molecules, such as adenosine, may mediate this effect.

Immune mechanisms in cerebral ischemic tolerance

Stressor-induced tolerance is a central mechanism in the response of bacteria, plants, and animals to potentially harmful environmental challenges. This response is characterized by immediate changes in cellular metabolism and by the delayed transcriptional activation or inhibition of genetic programs that are not generally stressor specific (cross-tolerance). These programs are aimed at countering the deleterious effects of the stressor. While induction of this response (preconditioning) can be established at the cellular level, activation of systemic networks is essential for the protection to occur throughout the organs of the body. This is best signified by the phenomenon of remote ischemic preconditioning, whereby application of ischemic stress to one tissue or organ induces ischemic tolerance (IT) in remote organs through humoral, cellular and neural signaling. The immune system is an essential component in cerebral IT acting simultaneously both as mediator and target. This dichotomy is based on the fact that activation of inflammatory pathways is necessary to establish IT and that IT can be, in part, attributed to a subdued immune activation after index ischemia. Here we describe the components of the immune system required for induction of IT and review the mechanisms by which a reprogrammed immune response contributes to the neuroprotection observed after preconditioning. Learning how local and systemic immune factors participate in endogenous neuroprotection could lead to the development of new stroke therapies.

Neuroprotection in stroke: past, present, and future

Stroke is a devastating medical condition, killing millions of people each year and causing serious injury to many more. Despite advances in treatment, there is still little that can be done to prevent stroke-related brain damage. The concept of neuroprotection is a source of considerable interest in the search for novel therapies that have the potential to preserve brain tissue and improve overall outcome. Key points of intervention have been identified in many of the processes that are the source of damage to the brain after stroke, and numerous treatment strategies designed to exploit them have been developed. In this review, potential targets of neuroprotection in stroke are discussed, as well as the various treatments that have been targeted against them. In addition, a summary of recent progress in clinical trials of neuroprotective agents in stroke is provided.

Dynamic aspects of cerebral hypoxic preconditioning measured in an in vitro model

Preconditioning increases the neurons' resistance to subsequent hypoxia. An in vitro study was conducted to explore kinetic aspects of hypoxic preconditioning. Hippocampal slices were exposed to one single or repeated episodes of oxygen and glucose deprivation (OGD). The interval between OGD episodes varied between 30 min and 180 min. OGD led to a significant reduction in the population spike amplitude. Subsequent episodes of OGD did not result in a further reduction in the population spike amplitude if the interval between the episodes was ca. 60 min, which demonstrated that there were preconditioning effects. In the experiment using an interval of 30 min, population spike amplitude decreased after each OGD episode. The set-up described is useful for detecting damaging effects of OGD as well as preconditioning effects. A time window of ca. 60 min is required to induce protective mechanisms.

Necrotic cell death in Caenorhabditis elegans

Similar to other organisms, necrotic cell death in the nematode Caenorhabditis elegans is manifested as the catastrophic collapse of cellular homeostasis, in response to overwhelming stress that is inflicted either in the form of extreme environmental stimuli or by intrinsic insults such as the expression of proteins carrying deleterious mutations. Remarkably, necrotic cell death in C. elegans and pathological cell death in humans share multiple fundamental features and mechanistic aspects. Therefore, mechanisms mediating necrosis are also conserved across the evolutionary spectrum and render the worm a versatile tool, with the capacity to facilitate studies of human pathologies. Here, we overview necrotic paradigms that have been characterized in the nematode and outline the cellular and molecular mechanisms that mediate this mode of cell demise. In addition, we discuss experimental approaches that utilize C. elegans to elucidate the molecular underpinnings of devastating human disorders that entail necrosis.

Pharmacologic preconditioning: translating the promise

A transient, ischemia-resistant phenotype known as "ischemic tolerance" can be established in brain in a rapid or delayed fashion by a preceding noninjurious "preconditioning" stimulus. Initial preclinical studies of this phenomenon relied primarily on brief periods of ischemia or hypoxia as preconditioning stimuli, but it was later realized that many other stressors, including pharmacologic ones, are also effective. This review highlights the surprisingly wide variety of drugs now known to promote ischemic tolerance, documented and to some extent mechanistically characterized in preclinical animal models of stroke. Although considerably more experimentation is needed to thoroughly validate the ability of any currently identified preconditioning agent to protect ischemic brain, the fact that some of these drugs are already clinically approved for other indications implies that the growing enthusiasm for translational success in the field of pharmacologic preconditioning may be well justified.

The Akt pathway is involved in rapid ischemic tolerance in focal ischemia in Rats

Although the protective mechanisms of delayed ischemic preconditioning have received extensive studies, few have addressed the mechanisms associated with rapid ischemic postconditioning. We investigated whether ischemic tolerance induced by rapid preconditioning is regulated by the Akt survival signaling pathway. Stroke was generated by permanent occlusion of the left distal middle cerebral artery (MCA) plus 30 min or 1 h occlusion of the bilateral common carotid artery (CCA) in male rats. Rapid preconditioning performed 1h before stroke onset reduced infarct size by 69% in rats with 30 min CCA occlusion, but by only 19% with 1 h occlusion. After control ischemia with 30 min CCA occlusion, Western Blot showed that P-Akt was transiently increased while Akt kinase assay showed that Akt activity was decreased. Although preconditioning did not change P-Akt levels at 1h and 5h compared with control ischemia, it attenuated reduction in Akt activity at 5h in the penumbra. However, preconditioning did not change the levels of P-PDK1, P-PTEN, and P-GSK3β in the Akt pathway, all of which were decreased after stroke. At last, the PI3K kinase inhibitor, LY294002, completely reversed the protection from ischemic preconditioning. In conclusion, Akt contributes to the protection of rapid preconditionin against stroke.

Is there a place for cerebral preconditioning in the clinic?

Preconditioning (PC) describes a phenomenon whereby a sub-injury inducing stress can protect against a later injurious stress. Great strides have been made in identifying the mechanisms of PC-induced protection in animal models of brain injury. While these may help elucidate potential therapeutic targets, there are questions over the clinical utility of cerebral PC, primarily because of questions over the need to give the PC stimulus prior to the injury, narrow therapeutic windows and safety. The object of this review is to address the question of whether there may indeed be a clinical use for cerebral PC and to discuss the deficiencies in our knowledge of PC that may hamper such clinical translation.

Mechanisms of heterosynaptic metaplasticity

Synaptic plasticity is fundamental to the neural processes underlying learning and memory. Interestingly, synaptic plasticity itself can be dynamically regulated by prior activity, in a process termed 'metaplasticity', which can be expressed both homosynaptically and heterosynaptically. Here, we focus on heterosynaptic metaplasticity, particularly long-range interactions between synapses spread across dendritic compartments, and review evidence for intracellular versus intercellular signalling pathways leading to this effect. Of particular interest is our previously reported finding that priming stimulation in stratum oriens of area CA1 in the hippocampal slice heterosynaptically inhibits subsequent long-term potentiation and facilitates long-term depression in stratum radiatum. As we have excluded the most likely intracellular signalling pathways that might mediate this long-range heterosynaptic effect, we consider the hypothesis that intercellular communication may be critically involved. This hypothesis is supported by the finding that extracellular ATP hydrolysis, and activation of adenosine A2 receptors are required to induce the metaplastic state. Moreover, delivery of the priming stimulation in stratum oriens elicited astrocytic calcium responses in stratum radiatum. Both the astrocytic responses and the metaplasticity were blocked by gap junction inhibitors. Taken together, these findings support a novel intercellular communication system, possibly involving astrocytes, being required for this type of heterosynaptic metaplasticity.

Effect of remote ischemic preconditioning on cognitive function after off-pump coronary artery bypass graft: a pilot study

Background

Several studies have shown in animal models that remote ischemic preconditioning (rIPC) has a neuroprotective effect. However, a randomized controlled trial in human subjects to investigate the neuroprotective effect of rIPC after cardiac surgery has not yet been reported. Therefore, we performed this pilot study to determine whether rIPC reduced the occurrence of postoperative cognitive dysfunction in patients who underwent off-pump coronary artery bypass graft (OPCAB) surgery.

Methods

Seventy patients who underwent OPCAB surgery were assigned to either the control or the rIPC group using a computer-generated randomization table. The application of rIPC consisted of four cycles of 5 min ischemia and 5 min reperfusion on an upper limb using a blood pressure cuff inflating 200 mmHg before coronary artery anastomosis. The cognitive function tests were performed one day before surgery and again on postoperative day 7. We defined postoperative cognitive dysfunction as decreased postoperative test values more than 20% of the baseline values in more than two of the six cognitive function tests that were performed.

Results

In the cognitive function tests, there were no significant differences in the results obtained during the preoperative and postoperative periods for all tests and there were no mean differences observed in the preoperative and postoperative scores. The incidences of postoperative cognitive dysfunction in the control and rIPC groups were 28.6% (10 patients) and 31.4% (11 patients), respectively.

Conclusions

rIPC did not reduce the incidence of postoperative cognitive dysfunction after OPCAB surgery during the immediate postoperative period.

Does Na⁺/Ca²⁺ exchanger, NCX, represent a new druggable target in stroke intervention?

Stroke causes a rapid cell death in the core of the injured region and triggers mechanisms in surrounding penumbra area that leads to changes in concentrations of several ions like intracellular Ca²⁺, Na⁺, H⁺, K⁺, and radicals such as reactive oxygen species and reactive nitrogen species. When a dysregulation of homeostasis of these messengers occurs, it can trigger cell death. In particular, it is widely accepted that a critical factor in determining neuronal death during cerebral ischemia is progressive dysregulation of Ca²⁺, Na⁺, K⁺, and H⁺ homeostasis that activate several death pathways, including oxidative and nitrosative stress, mitochondrial dysfunction, protease activation, and apoptosis. In the last decade, several seminal experimental works are markedly changing the scenario of research of principal players of an ischemic event. Indeed, some plasma membrane channels and transporters, involved in the control of Ca²⁺, Na⁺, K⁺, and H⁺ ion influx or efflux and, therefore, responsible for maintaining the homeostasis of these four cations, might function as crucial players in initiation of brain ischemic process. Indeed, these proteins, by regulating ionic homeostasis, may provide the molecular basis underlying glutamate-independent Ca²⁺ and Na⁺ overload mechanisms in neuronal ischemic cell death and, most importantly, may represent more suitable molecular targets for therapeutic intervention. Recently, a great deal of interest has been devoted to clarify the role of the plasma membrane protein known as Na⁺/Ca²⁺ exchanger, a transporter able to control Na⁺ and Ca²⁺ homeostasis. In this review, the pathophysiological role of NCX and its implication as a potential target in stroke intervention will be examined.